Tuberculosis

Mycobacterium tuberculosis was observed by Robert Koch in 1882, who discovered the staining technique to see the bacterium.

In 1943, Selman A Waksman found the antibiotic effective against Mycobacterium tuberculosis. Streptomycin purified from streptomyces grieseus was administered to human in 1944.

Drug resistance in TB occurred as a result of tubercle bacillus mutations. Soon the resistant mutants appeared, prooving the antibiotic therapy unsuccessful. Therefore combination of drugs were used to solve the problem of antibiotic resisitance.

Multidrug reisistant tuberculosis– MDR TB is TB that is resisitant to atleast two of the best anti TB drugs, isoniazed and rifamycin which are called first line drugs.

Extensively drug resistant TB is defined as TB which is resistant to isoniazed and rifamycin plus resisitant to any fluoroquinolone and atleast one of three injectable second line drugs(amikacin, kanamycin or capreomycin.

MDR-TB varies from patients to patients.

Antibiotics such as para-aminosalicyclic acid  and streptomycin have been in use for more than 50 years.

Patients are required to take upto 15 pills a day, plus daily injections, for atleast six months.

Medical treatment is lengthy and protection through vaccination is today, as before is insufficient.

Every year nearly two million people die from the disease. The bacterium that cause TB are spread in airborne droplets when people with disease cough or sneeze.

TB is considered lung disease however it can attack other parts of body such as kidneys or the brain.

TB is highly contagious and is spread through air.

Mycobacterium tuberculosis is resisitant to disinfectants, desiccation and are difficult to stain with water based stain such as Gram.

Infection with tubercle bacillus is characterised by the formation of tubercles, hard nodules in the lungs when Mycobacterium tubercle enters the lungs the macrophages engulf the pathogen but are unable to digest the bacteria due to it’s waxy mycolic acid cell wall.

Mycobacteria begin to multiply within the macrophages, eventually killing the macrophages that protect the host.

The cycle continues as the bacteria released from dead macrophages are then engulfed by other macrophages.

The infected macrophages result in inflammatory response(heat, swelling, dilated capillaries)

The cells at the centre of the tubercle may eventually die, producing either an area of necrosis or an actual cavity.

Mycobacterium tuberculosis can be differentiated from most other mycobacteria by the production of niacin.

Mycobacterium tuberculosis is a Gram positive aerobic mycobacterium that divides every 16-20 hours. This is extremely slow as compared to other bacteria which tend to have division times measured in minutes(for example Ecoli can divide roughly every 20 minute.)

Mycobacterium tuberculosis are grown on lowenstein jensen media. Middlebrook media are used for faster culture.

Bacteria can takes weeks to grow on culture media.

The Polymerase chain reaction is the rapid method which provides results within hours from specimen of the patients.

TB refers only to disease caused by Mycobacterium tuberculosis.

Similar disease ocassionally result from M.bovis,M africanum, M.microti.

TB of tonsils, lymph node, abdominal organs, bones and joints was once commonly caused by ingestion of milk infected with M. bovis but such infection is largely eradicated in developed countries by slaughtering cows that test positive.

Cell wall of Mycobacterium tuberculosis contains peptidoglycan and complex lipids. 60% of the cell wall is lipid. The lipid fraction consisit of mycolic acid, cord factor and wax D.

Mycolic acid are hydrophobic molecules that affect permeability properties at cell surface.

Mycolic acid prevent attack of the Mycobacteria by cationic proteins, lysozyme and oxygen radicals in phagocytic granule.

Cord factor is toxic to mammalian cells.

Lipids cause resistance to many antibiotics and killing by acidic and alkaline compounds and resistance to lethal oxidation and survival inside the macrophages.

Mycolic acid give rigid cell shape to the bacteria.

The type of mycolic acid can be used to distinguish different Mycobacteria.

Mycolic acid isolated from Mycobacteria are called eumycolic acids which have elevated 60-90 carbon atoms.

Mycolic acids are complex hydroxylated branched chain fatty acids with elevated carbon numbers.

They may also contain diverse functional groups such as methoxy, keto, epoxy ester group and cyclopropane ring.

Mycolic acids containing a methoxy group with double bond or cyclopropane ring are known as methoxymycolic acids.

Mycolic acids containing an a methyl-branched ketone are known as ketomycolic acids and those containing an a-methyl-branch epoxide as epoxymycolic acids.

Mycolic acid known as wax esters contain a double bond or a cyclopropane ring and an internal ester group.

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